Biology Reference
In-Depth Information
Wanner (2006)
identified 170 odorant-receptor genes in the honey bee, a dra-
matic increase compared to the 62 and 79 genes found in
D. melanogaster
and
Anopheles gambiae
genomes.
Odors are received by olfactory receptors located on the antennae and
the maxillary palps, which send their axons to the antennal lobes in insect
brains. Each third antennal segment in
D. melanogaster
contains
≈
1300 olfac-
tory receptor cells and each maxillary palp carries 120 chemosensory neurons
(
Anholt et al. 2001
). These neurons project to 43 glomeruli in the antennal
lobe of the brain. From there, processed olfactory information is relayed to
the mushroom body and the lateral horn of the protocerebrum. Insect odorant
receptors are seven-transmembrane-domain proteins, but are not related to
G protein-coupled receptors (
Carey and Carlson 2011
).
It is thought that there are fewer than 100
types
of odor receptors in insects
(
Vosshall et al. 1999
), perhaps as few as 50 or 60 (
Vosshall et al. 2000
), and these
are different from those found in mammals (
Carey and Carlson 2011
). Mammals
have
>
10,000 different receptor types. Insect receptors consist of large multi-
gene families (
Clyne et al. 2000, Vosshall et al. 1999
). Once an odor or phero-
mone has activated the olfactory receptors, it needs to be deactivated. Several
enzymes have been found that appear to degrade odor stimulants, including
esterases, oxidases, and glutathione transferases (
Field et al. 2000
).
Drosophila melanogaster
is able to recognize and discriminate between a
large number of odors (
Vosshall 2001, Rutzler and Zwiebel 2005
). Because there
are as few as 50 or 60
types
of receptors, each olfactory sensory neuron responds
to several odorants, but responds maximally to one (
Dryer 2000
). Although the
average olfactory-receptor gene is expressed in 20 olfactory neurons, some
receptor genes are expressed in only two to three neurons. Seven olfactory
receptor genes are expressed solely in the maxillary palp (
Vosshall et al. 2000
).
The sequencing of the pea aphid,
Acyrthosiphon pisum
, genome allowed
Smadja et al. (2009)
to identify 79 putative odorant and gustatory receptor genes.
11.5.4 Behavior of
Apis mellifera
Mushroom bodies in the Hymenoptera are much larger than those in
Drosophila
, which may reflect the importance of mushroom bodies for social
behavior, learning, and memory in the honey bee (
Rinderer 1986, Rybak and
Menzel 1993, Meller and Davis 1996
).
Social Hymenoptera (ants, bees, and wasps) have complex behaviors, includ-
ing caring for their brood. Social bee species such as
Apis mellifera
feed, protect
